An absorptive metasurface based on film-coupled colloidal silver nanocubes is demonstrated. The metasurfaces are fabricated using simple dip-coating methods and can be deposited over large areas and on arbitrarily shaped objects. The surfaces show nearly complete absorption, good off-angle performance, and the resonance can be tuned from the visible to the near-infrared.

The metasurface concept has emerged as an advantageous reconfigurable antenna architecture for beam forming and wavefront shaping, with applications that include satellite and terrestrial communications, radar, imaging, and wireless power transfer. The metasurface antenna consists of an array of metamaterial elements distributed over an electrically large structure, each subwavelength in dimension and with subwavelength separation between elements. In the antenna configuration we consider here, the metasurface is excited by the fields from an attached waveguide. Each metamaterial element can be modeled as a polarizable dipole that couples the waveguide mode to radiation modes. Distinct from the phased array and electronically scanned antenna (ESA) architectures, a dynamic metasurface antenna does not require active phase shifters and amplifiers, but rather achieves reconfigurability by shifting the resonance frequency of each individual metamaterial element. Here we derive the basic properties of a one-dimensional waveguide-fed metasurface antenna in the approximation that the metamaterial elements do not perturb the waveguide mode and are non-interacting. We derive analytical approximations for the array factors of the 1D antenna, including the effective polarizabilities needed for amplitude-only, phase-only, and binary constraints. Using full-wave numerical simulations, we confirm the analysis, modeling waveguides with slots or complementary metamaterial elements patterned into one of the surfaces.

Employing artificially structured metamaterials provides a means of circumventing the limits of conventional optical materials. Here, we use transformation optics (TO) combined with nanolithography to produce a planar Luneburg lens with a flat focal surface that operates at telecommunication wavelengths. Whereas previous infrared TO devices have been transformations of free-space, here we implement a transformation of an existing optical element to create a new device with the same optical characteristics but a user-defined geometry.

We consider the design and modeling of metasurfaces that couple energy from guided waves to propagating wavefronts. This is a first step towards a comprehensive, multiscale modeling platform for metasurface antennas-large arrays of metamaterial elements embedded in a waveguide structure that radiates intro free-space-in which the detailed electromagnetic responses of metamaterial elements are replaced by polarizable dipoles. We present two methods to extract the effective polarizability of a metamaterial element embedded in a one-or two-dimensional waveguide. The first method invokes surface equivalence principles, averaging over the effective surface currents and charges within an element to obtain the effective dipole moments; the second method is based on computing the coefficients of the scattered waves within the waveguide, from which the effective polarizability can be inferred. We demonstrate these methods on several variants of waveguidefed metasurface elements, finding excellent agreement between the two, as well as with analytical expressions derived for irises with simpler geometries. Extending the polarizability extraction technique to higher order multipoles, we confirm the validity of the dipole approximation for common metamaterial elements. With the effective polarizabilities of the metamaterial elements accurately determined, the radiated fields generated by a metasurface antenna (inside and outside the antenna) can be found self-consistently by including the interactions between polarizable dipoles. The dipole description provides an alternative language and computational framework for engineering metasurface antennas, holograms, lenses, beam-forming arrays, and other electrically large, waveguide-fed metasurface structures.

No abstract

No abstract

We have developed a 3D Finite Difference Time Domain (FDTD) algorithm to model obliquely incident waves through arbitrary birefringent and dichroic media with transverse periodic boundaries. Beginning with arbitrary conductivity and permittivity tensors, we employed the split-field method (SFM) to enable broadband sources with oblique incidence. We terminate our boundaries with a uniaxial perfectly matched layer (UPML) in one dimension and periodic boundaries in the other two dimensions. The algorithm is validated via several case studies: a polarizer pair, a twisted nematic liquid crystal, and an array of conducting particles. Using this approach, we simulate for the first time polarization gratings with light obliquely incident in directions orthogonal to the grating vector (i.e., at oblique angles outside the normal diffraction plane).

Since the discovery of materials with negative refractive index, widely known as metamaterials, it has been possible to develop new devices that utilize a metamaterial's ability to control the path of electromagnetic energy. Of particular promise, and already under intensive development for commercial applications, are metamaterial antennas for satellite communications. Using reconfigurable metamaterials in conjunction with the principles of holography, these new antennas can electronically steer the high gain antenna beam required for broadband communications while not having any moving parts, being thinner, lighter weight, and less expensive, and requiring less power to operate than conventional alternatives. Yet, the promise of these devices will not be realized without efficient and effective control and optimization. Toward this end, in this paper a discrete-dipole approximation (DDA) model of a waveguide-fed planar metamaterial antenna is derived. The proposed model is demonstrated to accurately predict the radiation of a two-dimensional metamaterial at a much reduced computational cost to full-wave simulation and at much greater fidelity than simpler models typically used in the field. The predictive capabilities of the derived DDA model opens possibilities for model-based control design for optimal beam steering.